The invention relates to the improvement of measurement accuracy in a network of intelligent power distribution units. More specifically, the invention relates to improving the comparability of current, voltage or power measurements carried out by intelligent power distribution units in a network. In its most immediate sense, the invention relates to improved synchronization of measurements carried out by networked intelligent power distribution units.
A data center is a facility housing computer systems in standardized racks. Each rack will contain one or more discrete electronic components (such as servers, switches, storage devices, power supplies, and others) that are vertically stacked. A rack unit or U (less commonly RU) is a unit of measure used to describe the vertical position of an electronic component within a standard-sized rack. One rack unit is 1.75 inches in height, and the physical location of an electronic component within the data center is typically specified by identifying the number of the rack in which the electronic component is mounted together with the a rack vertical number that identifies the vertical position of the electronic component within that rack (for example, a component may be located at a 7 U position).
Intelligent Power Distribution Units (“iPDUs”) are used in data centers to distribute power to the discrete electronic components. In a typical data center, power runs from a UPS, to a transformer, to a floor or wall PDU to a rack PDU such as an iPDU. Each iPDU has a plurality of female line power outlets, making it possible to supply power to a like plurality of electronic components.
The iPDUs are referred to as “intelligent” because they can typically connected to a network and are capable of sending information and receiving commands. For example, an iPDU may communicate via the Simple Network Management Protocol (“SNMP”) over a network. Additionally an iDPU can typically collect data regarding current, voltage and/or power at the unit or outlet level. Conventionally, a data center operator notes the location (rack number, rack vertical number) of each electronic component in the data center and also notes the particular iPDU and outlet that supply power to that electronic component. Thus the operator of the data center can monitor the power consumption of each electronic component in the data center by collecting current, voltage, and/or power data at the corresponding iPDU and outlet and sending this information to an energy management system.
FIG. 1 shows a prior art data center system 100. It include PowerIQ® server 102. PowerIQ is an energy management software application. It allows the system administrator of a data center to collect data from the many iPDUs in the data center, to analyze that data, and to send commands to the iPDUs over an SNMP network 128. PowerIQ may be a separate server appliance 102 as shown, or may run as an application on a server. Rack 104 is shown with servers 106, 108, and 110 mounted in it. iPDU 112 (shown separated from the rear of the rack 104 for clarity) supplies power to the servers 106, 108, and 110. Data connection 114 is connected to network 128, which is in turn connected by data connection 130 to PowerIQ server 102. Similarly, rack 116 is shown with severs 118, 120, and 122 mounted in it. iPDU 124 (shown separated from the rear of the rack 124 for clarity) supplies power to the servers 118, 120, and 122. Data connection 126 is connected to network 128. Although for illustrative purposes only two racks are shown in FIG. 1, a data center can contain thousands of racks and iPDUs, and tens of thousands of electronic components.
FIG. 2 of the present application shows the functioning of the prior art system shown in FIG. 1. If a user of the PowerIQ energy management system wishes to collect data from a set of iPDUs, the PowerIQ server 102 will issue a command to those iPDUs. (For simplicity, FIG. 2 considers only two iPDUs, specifically iPDUs 112 and 124.) The command will specify the measurement to be carried out and the duration of the measurement. Common measurements are:                average current consumption during a predetermined interval;        minimum current consumption during a predetermined interval;        maximum current consumption during a predetermined interval;        instantaneous current consumption at the end of a predetermined interval;        average voltage during a predetermined interval;        minimum voltage during a predetermined interval;        maximum voltage during a predetermined interval;        instantaneous voltage at the end of a predetermined interval;        average power consumption during a predetermined interval;        minimum power consumption during a predetermined interval;        maximum power consumption during a predetermined interval;        instantaneous power consumption during a predetermined interval;and a typical measurement duration is 300 seconds (although measurement durations can be as short as XXXXXX seconds and as long as YYYYY seconds).        
FIG. 2 shows PowerIQ server 102 issuing sampling command 202 over the network 128. In the illustrative example of FIG. 2, the sampling command 202 is received by iPDU 124 at time 218, which is before time 208, which is when the sampling command 202 is received by iPDU 112. This time difference (“skew”) can come about as a result of factors well understood to those skilled in the networking arts, such as distance, bandwidth, traffic, etc. At time 208 iPDU 112 begins to measure the variable whose trace is shown as trace 204. The variable could be current, voltage or power. During the interval 210 the iPDU measures this variable, and at the end of interval 210, the iPDU then stores in a ring buffer the measured average, minimum, maximum or instantaneous value of that variable, together with a time stamp, iPDU identification data, and the outlet number if outlet level metering is being used. Similarly, at time 218 iPDU 124 begins to measure the variable whose trace is shown as trace 206. This likewise could be current, voltage or power, but in the present example the sampling command 202 commands both the iPDUs 112, 124 to carry out the same measurement. During the interval 220 the iPDU 124 measures this variable, and at the end of interval 220, the iPDU then stores the measured data in a ring buffer together with a time stamp, iPDU identification data, and the outlet number if outlet level metering is being used.
The skew between time 208 and time 218 causes inconsistency in the measurements carried out by the iPDUs 112, 124 and therefore makes the measurements carried out by the iPDUs 112, 124 non-comparable. For example, if the iPDUs 112, 124 were commanded to measure maximum current, then during the intervals 210 and 220 the iPDUs 112, 124 would record different maximum currents even when (as illustrated) the currents measured vary identically with time. This can be understood because the current peak 228 is within the first interval 210 carried out by iPDU 112 and the corresponding current peak 230 is not within the interval 220 carried out by iPDU 124. Thus, the skew between time 208 and time 218 causes a comparison of the maximum current measured by the iPDU 112 with the maximum current measured by the iPDU 124 to have only a limited significance.
Further, even if the iPDUs 112, 124 received the sampling command 202 at the same time (i.e. even if the skew between times 208 and 218 were to be zero) the apparent synchrony indicated by the time stamps sent to the PowerIQ energy management system would not be meaningful. This is because the two iPDUs 112, 124 are not synchronized with each other and identical time stamps from these two iPDUs 112, 124 would not in fact indicate that they received the sampling command 202 simultaneously.
The PowerIQ energy management system periodically polls the ring buffer of each iPDU such as the iPDUs 112, 124. As shown in FIG. 2, the PowerIQ energy management system begins to poll the iPDUs at time 232, continues polling during interval 236, and concludes polling at time 234.
There remains a need in the art to improve the synchronization of measurements made by the iPDUs monitored by an energy management system so that comparisons between the data measured by the iPDUs are meaningful.